The geocoronal responses to the geomagnetic disturbances

M. Kuwabara, K. Yoshioka, G. Murakami, F. Tsuchiya, Tomoki Kimura, A. Yamazaki, I. Yoshikawa

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


Atomic hydrogen atoms in the terrestrial exosphere resonantly scatter solar Lyman alpha (121.6 nm) radiation, observed as the hydrogen geocorona. Measurements of scattered solar photons allow us to probe time-varying distributions of exospheric hydrogen atoms. The Hisaki satellite with the extreme ultraviolet spectrometer (EXtreme ultraviolet spectrosCope for ExosphEric Dynamics: EXCEED) was launched in September 2013. EXCEED acquires spectral images (52–148 nm) of the atmospheres/magnetospheres of planets from Earth orbit. Due to its low orbital altitude (~1000 km), the images taken by the instrument also contain the geocoronal emissions. In this context, EXCEED has provided quasi-continuous remote sensing observations of the geocorona with high temporal resolution (~1 min) since 2013. These observations provide a unique database to determine the long-term behavior of the exospheric density structure. In this paper, we report exospheric structural responses observed by EXCEED to geomagnetic disturbances. Several geomagnetic storms with decreases of Dst index occurred in February 2014 and the Lyman alpha column brightness on the night side of the Earth increased abruptly and temporarily by approximately 10%. Hisaki reveal that the time lag between the peaks of the magnetic activity and the changes in the Lyman alpha column brightness is found to be about 2 to 6 h during storms. In order to interpret the observational results, we evaluate quantitatively the factors causing the increase. On the basis of these results, a coupling effect via charge exchange between the exosphere and plasmasphere causes variations of the exospheric density structure.

Original languageEnglish
Pages (from-to)1269-1276
Number of pages8
JournalJournal of Geophysical Research: Space Physics
Issue number1
Publication statusPublished - 2017 Jan 1


  • Hisaki
  • Lyman alpha
  • exosphere
  • geocorona
  • hydrogen
  • magnetic storm

ASJC Scopus subject areas

  • Space and Planetary Science
  • Geophysics


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